Method of making a fibre-reinforced molded racquet frame

ABSTRACT

A method of making a fibre-reinforced molded racquet frame is disclosed. The method comprises placing two cores each including a respective tube having at least one layer of woven reinforcing fibres in a mold shaped to define the frame. A respective core is positioned on each side of the split-line of the mold. A plurality of string-securing members are formed with each string-securing member comprising a first portion shaped to receive and position at least one string of stringing to be secured in the frame and a second portion adapted to be embedded in the frame. The string-securing member is supported such that, upon closure of the mold, the second portions are disposed inside the mold cavity and entrapped between the two cores while the first portions project out of the mold cavity into the area which will be surrounded by the mold frame. A plastics material is injected into the mold around the cores and the second portions of the string-securing members. The plastics material preferably has a relatively low setting temperature and a relatively low viscosity.

This application is a continuation of application Ser. No. 838,791,filed Mar. 12, 1986 now abandoned.

TECHNICAL FIELD

This invention relates to racquets for use in games such as tennis,squash, racquet-ball and the like. The invention is more particularlyconcerned with methods of making fibre-reinforced molded racquet frames.

BACKGROUND OF THE INVENTION

It is known to mold racquet frames in fibre-reinforced thermoplasticsmaterial, with the fibre reinforcement taking the form of continuousfilamentary material woven into a fabric or braid. However, currentlyavailable methods of producing such molded racquet frames suffer from anumber of disadvantages. For example, they are rather time-consuming,firstly because the fibres normally have to be pre-impregnated with theepoxy or polyester resin into which they are to be molded. Thepre-impregnated fibres are then laid in the mold, which is closed andheated to an elevated temperature while further epoxy or polyester resinis injected and allowed to cure (or set). This process typically takesover an hour, during which at least some resin usually escapes from themold. As a result of this, and of the fact that the resin is fairlyviscous, the surface finish of racquet frames made by the known methodsis usually rather poor, so that, on removal from the mold, furthersurface finishing operations such as deflashing, filling voids andholes, polishing and/or coating are necessary to render the appearanceof the frames acceptable. Additionally, it can be difficult to provideframes molded by these methods with stringing holes or otherstring-supporting structures.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide methods ofmaking fibre-reinforced molded racquet frames in which some or all ofthe above-mentioned disadvantages are alleviated.

According to one aspect of the invention, there is provided a method ofmaking a fibre-reinforced molded racquets frame, the method comprisingplacing at least one core including a tube comprising at least one layerof woven reinforcing fibres in a mold shaped to define the frame, andinjecting a plastics material having a relatively low settingtemperature and a relatively low viscosity, such as a methacrylate-basedresin, into the mold around the core or cores.

Because the plastics material has a relatively low viscosity, it notonly penetrates the weave of the reinforcing fibres, but also forms athin layer between the outside of the tube of fibres and the walls ofthe mold cavity. This layer has the result that the molded racquet framealready has a good surface finish when it is removed from the mold.

Each core can further comprise an inflatable tube disposed inside thetube of reinforcing fibres, in which case the method can further includethe steps of inserting the inflatable tube, either uninflated orslightly inflated, into the tube of reinforcing fibres prior to placingthe core in the mold, and maintaining the inflatable tube inflatedduring the injection and setting of the plastics material.

Alternatively and preferably, each core can comprise a plastics foamcore member, advantageously an extruded polyethylene foam core member,disposed inside the tube of reinforcing fibres, in which case the methodcan advantageously further include the step of weaving the tube ofreinforcing fibres, preferably in the form of a braid, around the coremember.

The reinforcing fibres can be carbon fibres, boron fibres, glass fibres,silicon carbide fibres or aramid fibres of the kind available under thetrademark Kevlar, or any combination of these.

Where the tube of reinforcing fibres is woven into a braid, it ispreferably woven in at least two contrasting colors, for example byusing black carbon fibres and yellow Kevlar fibres. This has the effectof producing a striking finished appearance for the frame, as willbecome apparent hereinafter.

In a preferred implementation of the method, two cores are laid in themold, one on each side of the split-line thereof, and the method furtherincludes the steps of producing a plurality of string-securing memberseach comprising a first portion shaped to receive and position at leastone string of the stringing to be secured in the frame and a secondportion adapted to be embedded in the frame, and, prior to saidinjecting step, supporting the string-securing members such that saidsecond portions are disposed inside the mold cavity between the twocores while the first portions project out of the mold cavity into thearea which will be surrounded by the molded frame.

Preferably, each string-securing member comprises a generally U-shapewire loop having the upper ends of the limbs of its U-shape bent over,whereby the bent over upper ends of the loop constitute said secondportion of the string-securing member.

According to another aspect of the invention, there is provided a methodof making a fibre-reinforced molded racquet frame, the method comprisingplacing at least one core including the reinforcing fibres in a moldshaped to define the frame, and injecting a plastics material into themold around the core, wherein said core is produced by weaving a tube ofreinforcing fibres around an elongate plastics foam core member.

The plastics foam is preferably polyethylene foam, and the core memberis preferably formed by extrusion, while the plastics material injectedinto the mold and the fibres may take any of the forms specified inrelation to the first aspect of the invention. Additionally, astring-securing member or members can be provided as described inrelation to the first aspect of the invention.

According to a further aspect of the invention, there is provided amethod of making a fibre-reinforced molded racquet frame, the methodcomprising placing two cores each including a respective tube comprisingat least one layer of woven reinforcing fibres in a mold shaped todefine the frame, a respective core being positioned on each side of thesplit-line of the mold, producing a plurality of string-securing memberseach comprising a first portion shaped to receive and position at leastone string of the stringing to be secured in the frame and a secondportion adapted to be embedded in the frame, supporting thestring-securing members such that said second portions are disposedinside the mold cavity between the two cores while the first portionsproject out of the molded frame, and injecting a plastics material intothe mold around the cores and said second portions of thestring-securing members.

The injected plastics material, the reinforcing fibres, the cores andthe string-securing members can take any of the forms specified inrelation to the first aspect of the invention.

The invention also includes racquet frames made by any of the methods ofthe above-mentioned aspects of the invention, and racquets incorporatingsuch frames.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings, of which:

FIG. 1 is an exploded perspective view of a mold for making afibre-reinforced molded racquet frame by a method in accordance with thepresent invention;

FIG. 2 is a detailed perspective view, partially in section, of the partof the racquet frame being molded in the mold of FIG. 1, at an earlystage in the molding process; and

FIG. 3 is a plan view of the part of the finished racquet frame moldedin the mold of FIG. 1, but with the string-securing wire omitted for thesake of simplicity.

DETAILED DESCRIPTION OF THE INVENTION

The mold shown in FIG. 1 is designated generally by reference 10, and isintended for molding a racquet frame of the kind shown at 11. As can beseen in FIG. 1, mold 10 comprises four principal parts, namely upper andlower complementary mold plates 12 and 14, which together define thebasic mold cavity 16 in which the racquet frame 11 is molded, and upperand lower locating members 18, 20. Locating members 18, 20 togetherdefine a cassette for precisely locating and supporting a one-piecesinuous titanium wire string-securing member 21 which is to be moldedinto racquet frame 11. Mold 10, string-securing member 21 and the waythe latter is located and supported with respect to mold 10 aresubstantially described in United Kingdom Patent Application No.8426226. However, racquet frame 11, and the precise method by which itis molded in the mold 10 differ from the frame and method described inthat application in several important respects, as follows.

Firstly, frame 11 is reinforced by continuous woven reinforcing fibres,preferably a combination of carbon fibres for tensile and flexuralstrength and Kevlar fibres for impact resistance. The carbon fibres areblack, while the Kevlar fibres are yellow, and respective bundles ofboth fibres are preferably woven together into a multi-layer tubularbraid 24 having a strikingly zig-zag striped appearance of the kindshown in FIGS. 2 and 3. Braid 24 forms part of a core 26, which isproduced by weaving successive layers of fibres, each layer containingboth kinds of fibres, onto an extruded polyethylene foam core member 28,until a braided tube, four or five layers thick, is woven onto the coremember.

The weaving technique involved is known per se, e.g., for the weaving ofboot- or shoe-laces on a fibre core, and involves pulling the coremember 28 along the center line or axis of a multi-spindle braidingmachine while weaving the first layer therearound, then passing the coremember with the first layer of braid on it through the same braidingmachine again to weave the second layer therearound, and so on. To giveadded tensile strength, a layer of longitudinally-extending fibres isapplied to core 26, preferably between the penultimate and the finalbraided layers.

The weaving of braid 24 onto core member 28 ensures an extremely tightfit therebetween, so that the braid and core member form an almostintegral structure with significantly greater integration between thebraid and the core member than can be achieved by simply inserting thelatter into the former after weaving (particularly bearing in mind thatif the braid were separately woven to be such a tight fit on the coremember, it would probably not then be possible to insert the core memberinto it).

It will be appreciated that core 26 can be continuously produced asdescribed above to form considerable continuous lengths thereof, whichare typically wound onto drums. Then, when required, any desired lengthof core 26 is simply unwound and cut from the drum.

To mold racquet frame 11, a first cut length 26a of core 26 is placed inthe portion of mold cavity 16 in upper mold plate 12, and a second cutlength 26b of core 26 is placed in the portion of the mold cavity in thelower mold plate 14: the walls of the mold cavity are previously sprayedwith a releasing agent, and it has been found that this assists inholding the cores 26a and 26b in their respective halves of the moldcavity. String-securing member 21 is then mounted in the cassettedefined by locating members 18, 20, as described in the aforementionedUK patent application, and a bundle of reinforcing fibres (preferablycarbon fibres) may, if desired, be interwoven with portions 22 ofstring-securing member 21 protruding from the cassette (i.e., theportions intended to be disposed in mold cavity 16). Mold 10 is thenassembled, i.e. closed, as also descibed in the aforementioned UK patentapplication, with the result that the portions 22 of the member 21disposed within the mold cavity 16, and the reinforcing fibres woventherearound, are trapped between cores 26a and 26b as shown in FIG. 2.As mold 10 is closed, cores 26a and 26b tend to be compressed againsteach other and around portions 22 of member 21, which ensures thatmember 21 is firmly keyed into molded frame 11 as will become apparenthereinafter.

Once the mold 10 is assembled in its closed condition, a low viscosity,low temperature setting plastics material, for example, in the form of amethacrylate-based resin is injected into mold cavity 16 under pressure.We have found that a particularly suitable resin is that available fromthe Mond division of ICI under the trademark "Modar 835", which is ahigh molecular weight methacrylate-based resin in methyl methacrylatesolution. It has a viscosity of 40 cps at 20° C. The resin is typicallyinjected at a pressure of 30 p.s.i. and maintained at a temperature ofabout 20° C. during curing (or setting), under which conditions it sets,and mold 10 can be opened to remove molded frame 11, in about fourminutes. However, if the resin is maintained at the higher temperatureof about 85° C., it sets in about one minute.

Because of its low viscosity, the methacrylate resin not only penetratesthe weave of the reinforcing fibres of cores 26a and 26b and of thefibres woven around portions 22 of string-securing member 21, but alsoforms a thin layer between the cores on the one hand and the walls ofcavity 16. The penetration of the resin ensures that string-securingmember 21 is firmly keyed into the resulting molded racquet frame 11 bythe various reinforcing fibres. Additionally, the aforementionedformation of a thin layer of resin has the result that, when mold 10 isopened, the resulting molded racquet frame requires little or no furthersurface finishing to enhance its appearance. In fact, the molded frame11 has the rather striking appearance shown in FIG. 3, with a smoothfinish and the regular yellow and black zig-zag pattern of the braidclearly visible through the transparent resin: consequently, little orno further surface finishing is necessary. All that remains to completethe racquet, therefore, is fitting a suitable grip (not shown) on handlepart 30 of molded frame 11, and securing the stringing (not shown) tostring-securing member 21.

It will be appreciated that the above described method of making racquetframe 11 has a number of advantages. Primarily, it is relatively fastand clean, and produces a racquet frame that needs little or no furthersurface finishing and can if desired have a striking appearance.Additionally, the use of carbon and Kevlar reinforcing fibres means thatracquet frame 11 is light and strong, with a good impact resistance.Most importantly, test have shown that even without the further bundleof reinforcing fibres wound around string-securing member 21, the forcerequired to pull this member from molded frame 11 was extremely large,so large in fact that, on occasions, the wire simply broke before itcould be pulled out.

Many modifications can be made to the above-described method of makingracquet frame 11. For example, reinforcing fibres other than carbon andKevlar can be used, e.g., glass fibres, silicon carbide fibres or boronfibres, either on their own or in combination with each other. Variousdifferent weaving patterns and color combinations can also be used, toproduce different visual effects or patterns in the surface of thefinished frame, e.g., diamond patterns, pepper-and-salt patterns and soon. Also, cores 26a and 26b can be formed with hollow inflatable coremembers in place of the foam core member 28, this inflatable core memberbeing inserted into the braid 24 while uninflated or only partiallyinflated, and then fully inflated during the molding process.Furthermore, other suitable low temperature curing, low viscosity resinsor like plastics materials can be used in place of the specificmethacylate resin cited, including other resins in the "Modar" range ofresins offered by ICI. Indeed, a thermosetting plastics material canalso be used, but in that case, some of the advantages of theabove-described method of making the racquet frame 11 would be lost.

Another modification which can be made is to replace the singlestring-securing member 24 with a plurality of individual stringingloops, which can take any convenient form and need not be made fromwire: all that is required is a first portion to define a loop or eyefor the stringing and a second or root portion shaped to be embedded inmolded frame 11.

I claim:
 1. A method of making a fibre-reinforced molded racquet frame,the method comprising the steps of:forming two separate cores eachincluding a respective tube having at least one layer of wovenreinforcing fibres; forming a mold cavity within a mold in the shape ofthe racquet frame with a first portion of the mold cavity formed in anupper mold plate and a second portion of the mold cavity formed in alower mold plate; placing one of the cores in the first portion of themold cavity in the upper mold plate and placing the other of the coresin the second portion of the mold cavity in the lower mold plate withopposing surfaces of the cores facing one another; forming a pluralityof string-securing members with each string-securing member comprising afirst portion in the form of a loop and a second portion in the form ofan anchorage connected to the loop, the loop being shaped to receive andposition at least one string of stringing in the area between the loopand the inside surface of the molded frame; placing, while the first andsecond mold plates are separated, the second portion of eachstring-securing member in a position overlying the opposing surfaces ofthe cores with the first portions of each string-securing memberprojecting out of the mold cavity into the area which will be surroundedby the molded frame; closing the mold to place the opposing surfaces ofthe separate cores into contact with one another and into contact withthe second portions of the string-securing members; injecting a plasticsmaterial into the mold around the cores and the second portions of thestring-securing members; allowing the plastics material to harden in themold cavity to form to the molded racquet frame; and removing the moldedracquet frame formed of the cores, hardened plastics material andstring-securing members from the mold cavity.
 2. A method as claimed inclaim 1, wherein said injected plastics material is a plastics materialhaving a low setting temperature and a low viscosity.
 3. A method asclaimed in claim 2, wherein said injected plastics material is amethacrylate-based resin.
 4. A method as claimed in claim 1, whereineach core further comprises an inflatable tube disposed inside the tubeof reinforcing fibres, and wherein the method further includes the stepsof inserting the inflatable tube into the tube of reinforcing fibresprior to placing the core in the mold, and maintaining the inflatabletube inflated during the injection and setting of the plastics material.5. A method as claimed in claim 1, wherein each core further comprises aplastic foam core member disposed inside the tube of reinforcing fibres.6. A method as claimed in claim 5, wherein said plastics foam coremember is formed as an extruded polyethylene foam core member.
 7. Amethod as claimed in claim 5, further including the step of weaving eachlayer of reinforcing fibres around the core member.
 8. A method asclaimed in claim 6, further including the step of weaving each layer ofreinforcing fibres around the core member.
 9. A method as claimed inclaim 7, comprising successively weaving a plurality of layers ofreinforcing fibres around the core member, forming on said plurality oflayers a further layer of reinforcing fibres which extend parallel toeach other and substantially longitudinally of the core member, and thenweaving at least one outer layer of reinforcing fibres around the layerof longitudinally extending fibres.
 10. A method as claimed in claim 7,wherein each layer of woven reinforcing fibres is woven as a braid. 11.A method as claimed in claim 7, wherein the reinforcing fibres areselected and woven as tows of two contrasting colors.
 12. A method asclaimed in claim 7, wherein the reinforcing fibres are selected from thegroup consisting of carbon fibres, boron fibres, glass fibres, siliconcarbide fibres, aramid fibers, and combinations thereof.
 13. A method asclaimed in claim 1, wherein each string-securing member comprises agenerally U-shaped wire loop having the upper ends of the limbs of itsU-shape bent over, whereby the bent over upper ends of the loopconstitute said second portion of the string-securing member.
 14. Amethod as claimed in claim 13, wherein a plurality of saidstring-securing members are integrally formed by bending a single lengthof wire.
 15. A method as claimed in claim 14, further comprisingarranging further elongate reinforcing fibres to engage said upper endsof said limbs in the mold cavity, to be molded to the frame therewith.16. A method as claimed in claim 13, wherein said wire is titanium wire.17. A method as claimed in claim 1, wherein the plastics material is aresin.
 18. A method as claimed in claim 1, wherein the plastics materialis a polymer.
 19. A method as claimed in claim 4, wherein the insertingstep includes the inflatable tube being uninflated.
 20. A method asclaimed in claim 4, wherein the inserting step includes the inflatabletube being slightly inflated.
 21. A method as claimed in claim 1,wherein said forming includes the string-securing members being formedas a continuous one-piece structure.
 22. A method as claimed in claim 1,wherein said forming includes the string-securing members being formedas a plurality of individual stringing loops.